Cross-kingdom or interkingdom pathogenic microorganisms are now recognized more commonly (1, 2). There are an increasing number of organisms, and occasionally even the same strains of an organism, that can colonize and/or infect both plants and humans. Pathogenic microorganisms demonstrating cross-kingdom host ranges may have been overlooked for several reasons. Taxonomic name changes may have resulted in misidentification. In addition, a different name may have been used to describe the same microorganism (2, 3). A primary reason for this failure to recognize nontraditional pathogenic microorganisms may be due to little earlier knowledge that some plant pathogens can grow at temperatures of body extremities and external parts of the body, which may be as low as 33.2°C (4). The thermal growth tolerance for most fungi is significant at 37°C or below (5). Fungi associated with human disease are speculated to have originated from asymptomatic or diseased plants (6). However, mammalian defense systems of innate temperature are a potent nonspecific defense against most fungi (5) and bacteria. As to classification of cross-kingdom microorganisms, Hubalek (7) suggested that emerging human infectious diseases could be grouped into those transmissible between humans (anthroponoses), those transmissible from animals to humans (zoonoses), and those transmissible to humans from the environment as sapronoses. However, the term “sapronoses” was presented as those diseases having an environmental reservoir (organic matter, soil, and plants). Other treatises define sapronoses as diseases whose source is only an abiotic substrate (nonliving environment). Hubalek (7) did not address diseases of humans transmissible from plants, but the term “phytoses” has been used in presentations by the Centers for Disease Control and Prevention (CDC) (R. V. Tauxe, personal communication), although “phytonoses” would be consistent with Hubalek's classification system (7).

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